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12-Channel Gamma Buffers with VCOM Buffer ADD8702
FEATURES Programmable 12-Channel Gamma Reference Generator Mask Programmable Adjustable VCOM Buffer Upper/Lower Outputs Swing to VDD/GND Continuous Output Current: 10 mA VCOM Peak Output Current: 250 mA Outputs with Fast Settling Time for Load Change Output Pins Are Compatible with ADD8701 Single-Supply Operation: 7 V to 16 V Supply Current: 15 mA Max APPLICATIONS TFT LCD Panels FUNCTIONAL BLOCK DIAGRAM
VCOM OUT VGMA12 VGMA11 VGMA10 VGMA9 VGMA8
26
32
31
30
26
28
27
25 24 23 22 21 20 19 18 17
VDD VCOM ADJ VHIGH VIN11 VIN10 VIN9 VIN8 VIN7
VGMA7
GND
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
GND VDD VGMA6 VGMA5 VGMA4 VGMA3 VGMA2 VGMA1
VLOW
VIN6
VIN5
VIN4
VIN3
VIN2
VDD
The ADD8702 is a low cost, mask programmable, 12-channel gamma reference generator, plus an adjustable VCOM driver. This part is designed to provide gamma correction for high resolution TFT LCD panels. The 12 gamma reference levels and VCOM are mask programmable to 0.3% resolution using the on-chip 500 chain resistor string. This reduces component and board costs. The ADD8702 provides a complete programmed set of gamma voltage references for the LCD source drivers. These references settle quickly to load change. The VCOM output is stable with high capacitive loads and can source or sink 250 mA peak current. The VCOM output level can be adjusted using an external trim-potentiometer or discrete resistors.
The output pins are compatible with the ADD8701. This allows for single board design and fast turns for prototyping using the initial ADD8701 board design. The ADD8702 is specified over the temperature range of -40C to +85C and comes in the 32-lead lead frame chip scale package (LFCSP) for compact board space.
PANEL TIMING CONTROLLER
ADD8702
TIMING AND CONTROL GAMMA REFERENCE VOLTAGES GAMMA VCOM
SCAN DRIVER CONTROL
SOURCE DRIVER NO. 1 384
SOURCE DRIVER NO. 2 384
SOURCE DRIVER NO. 8 384
RGB SCAN DRIVERS 768 TFT COLOR PANEL 1024 768
Figure 1. Typical SVGA TFT LCD Application
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) 2003 Analog Devices, Inc. All rights reserved.
GND
GENERAL DESCRIPTION
ADD8702-SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (V
Parameter OUTPUT ACCURACY VSYSTEM ERROR MASK PROGRAMMABLE RESISTOR STRING Total Resistor String Resistor Matching OUTPUT CHARACTERISTICS Output Voltage High (VGMA11, VGMA12) Output Voltage Mid (VGMA3 to VGMA10) Output Voltage Low (VGMA1, VGMA2) Continuous Output Current Peak Output Current Settling Time--Voltage VCOM CHARACTERISTICS Continuous Output Current Peak Output Current Settling Time--Voltage SUPPLY CHARACTERISTICS Supply Voltage Power Supply Rejection Ratio SUPPLY CURRENT Symbol VSY ERROR
DD
= 16 V, TA = 25 C, unless otherwise specified.)
Min Typ 10 Max 50 Unit mV
Conditions
RTOTAL RMATCH VOUT VOUT VOUT IOUT IPK tS IOUT IPK tS VDD PSRR ISYS
500 Elements VLOW to VHIGH Any Two Segments IL = 100 A IL = 5 mA -40C TA +85C IL = 5 mA IL = 100 A IL = 5 mA -40C TA +85C 1 V Step 0.1%, RL = 10 k, CL = 200 pF
22.5 1 15.995 15.95 14.6 5 50 10 150 1 35 250 0.8 7 68 16 75 11 15 16
k % V V V V mV mV mV mA mA s mA mA s V dB mA mA
15.85 15.75
150 250
1 V Step 0.1%, RL = 10 k, CL = 200 pF
VS = 6 V to 17 V, -40C TA +85C No Load -40C TA +85C
Specifications subject to change without notice.
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ADD8702
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (VS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V Storage Temperature Range . . . . . . . . . . . . . -65C to +150C Operating Temperature Range . . . . . . . . . . . . -40C to +85C Junction Temperature Range . . . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering, 60 sec.) . . . . . . . . 300C ESD Tolerance (HBM) . . . . . . . . . . . . . . . . . . . . . . . 1,000 V
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Package Type 32-Lead LFCSP (CP)
JA
1
2 JB
Unit C/W
35
13
NOTES 1 JA is specified for worst-case conditions, i.e., JA is specified for device soldered in circuit board for surface-mount packages. 2 JB is applied for calculating the junction temperature by reference to the board temperature.
ORDERING GUIDE
Model ADD8702ACP-R2 ADD8702ACP-REEL ADD8702ACP-REEL7
Temperature Range -40C to +85C -40C to +85C -40C to +85C
Package Description 32-Lead LFCSP 32-Lead LFCSP 32-Lead LFCSP
Package Option CP-32 CP-32 CP-32
PIN CONFIGURATION
32 VCOM OUT 31 GND 30 VGMA12 29 VGMA11 28 VGMA10 27 VGMA9 26 VGMA8 25 VGMA7
VDD 1 VCOM ADJ 2 VHIGH 3 VIN11 4 VIN10 5 VIN9 6 VIN8 7 VIN7 8
PIN 1 INDICATOR
ADD8702
TOP VIEW
24 GND 23 VDD 22 VGMA6 21 VGMA5 20 VGMA4 19 VGMA3 18 VGMA2 17 VGMA1
PIN FUNCTION DESCRIPTIONS
Pin No. 1, 15, 23 2 3 4-13 14 16, 24, 31 17-22, 25-30 32
Mnemonic VDD VCOM ADJ VHIGH VIN11-VIN2 VLOW GND VGMA1-VGMA12 VCOM OUT
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADD8702 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
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VIN6 9 VIN5 10 VIN4 11 VIN3 12 VIN2 13 VLOW 14 VDD 15 GND 16
Description Power (+) VCOM Adjust Input Highest Gamma Input Voltage Gamma Buffer Inputs Lowest Gamma Input Voltage Power (-) Gamma Buffer Outputs VCOM Buffer Output
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ADD8702-Typical Performance Characteristics
12 TA = 25 C 10
12 VDD = 16V 11 SUPPLY CURRENT (mA)
10 VDD = 16V GAMMA 1 TO 9 0 2k , 10k
SUPPLY CURRENT (mA)
10 9 8 7
-30
8
GAIN (dB)
-10 150 -20
6
4
2
6 5 -40
-40 100k
0
0
4 8 12 SUPPLY VOLTAGE (V)
16
25 TEMPERATURE ( C)
85
1M 10M FREQUENCY (Hz)
30M
TPC 1. Supply Current vs. Supply Voltage
TPC 2. Supply Current vs. Temperature
TPC 3. Frequency Response vs. Resistive Loading
10 VDD = 16V GAMMA 10 TO 12 0 2k , 10k
10 VDD = 16V VCOM 2k , 10k -10
20 VDD = 16V GAMMA 1 TO 9 10 50pF
150
0
GAIN (dB)
GAIN (dB)
GAIN (dB)
-10 150 -20
0 340pF -10 540pF 100pF
-20
-30 -30
-40
-20 1040pF
-40 100k
1M 10M FREQUENCY (Hz)
30M
-50 100k
1M 10M FREQUENCY (Hz)
30M
-30 100k
1M 10M FREQUENCY (Hz)
30M
TPC 4. Frequency Response vs. Resistive Loading
TPC 5. Frequency Response vs. Resistive Loading
TPC 6. Frequency Response vs. Capacitive Loading
20 VDD = 16V GAMMA 10 TO 12 10
20 VDD = 16V VCOM
180 160
PHASE SHIFT (Degrees)
10
VDD = 16V GAMMA 1 TO 12 RL = 2k
GAMMA 12 GAMMA 1
140 120 100 80 60 40
GAIN (dB)
340pF -10 540pF -20 1040pF -30 100k
100pF
GAIN (dB)
0
50pF
0
-10 340pF 100pF -20 540pF 1040pF 50pF 30M
1M 10M FREQUENCY (Hz)
30M
-30 100k
1M 10M FREQUENCY (Hz)
0
200
400 600 800 1,000 CAPACITIVE LOAD (pF)
1,200
TPC 7. Frequency Response vs. Capacitive Loading
TPC 8. Frequency Response vs. Capacitive Loading
TPC 9. Input and Output Phase Shift vs. Capacitive Load
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ADD8702
16
VDD = 16V RL = 10k CL = 100pF
14 12
VDD = 16V RNULL = 33 CL = 100pF
10 VCOM SLEW RATE FALLING 8 VCOM SLEW RATE RISING 6 4 2 0 -40
VOLTAGE (20mV/DIV)
SLEW RATE (V/ s)
VOLTAGE (2V/DIV)
7V < V DD < 16V RNULL = 33 CL = 0.1 F
25 TEMPERATURE ( C) 85
TIME (2 s/DIV)
TIME (20 s/DIV)
TPC 10. Large Signal Transient Response
TPC 11. Slew Rate vs. Temperature
TPC 12. Small Signal Transient Response
11 10 9 8 VDD = 16V GAMMA = 2
11 10 9 VDD = 16V GAMMA = 11
11 10 9 VDD = 16V VCOM
AMPLITUDE (V)
7 6 5 4 3 2 1 0 -200
AMPLITUDE (V)
AMPLITUDE (V)
120pF 320pF 1 F 10 F
8 7 6 5 4 3 2 1
320pF 120pF 1 F 10 F
8 7 6 5 4 3 2 1
120pF 320pF 1 F 10 F
520pF
520pF
520pF
200
600 1,000 TIME (ns)
1,400
1,800
0 -200
200
600 1,000 TIME (ns)
1,400
1,800
0 -200
200
600 1,000 TIME (ns)
1,400
1,800
TPC 13. Transient Load Response vs. Capacitive Load
TPC 14. Transient Load Response vs. Capacitive Load
TPC 15. Transient Load Response vs. Capacitive Load
100
OUTPUT VOLTAGE ERROR (mV)
OUTPUT VOLTAGE ERROR (mV)
80 70 60 50 SINK 40 30 20 10 0 0.001 0.01 0.1 1 10 LOAD CURRENT (mA) 100 SOURCE
OUTPUT VOLTAGE ERROR (mV)
VDD = 16V 90 GAMMA 1 TO 9
1,400 1,200 1,000 800 600 400 200
VDD = 16V GAMMA 10 TO 12 SINK
50 VDD = 16V 45 VCOM 40 35 30 25 20 SOURCE 15 10 SINK 5 0 0.001
SOURCE
0 0.001
0.01 0.1 1 10 LOAD CURRENT (mA)
100
0.01 0.1 1 10 LOAD CURRENT (mA)
100
TPC 16. Output Voltage Error vs. Load Current
TPC 17. Output Voltage Error vs. Load Current
TPC 18. Output Voltage Error vs. Load Current
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ADD8702
6,000
80
POWER SUPPLY REJECTION RATIO (dB)
FREQUENCY (No. of Amplifiers)
VDD = 16V TA = 25 C 5,000 ALL CHANNELS 4,000
60 40 20 0 -20 -40
ALL CHANNELS VDD = 8V TA = 25 C
VOLTAGE (3V/DIV)
3,000
2,000
PSRR -60 -80 -100 -120 100 1k 10k 100k FREQUENCY (Hz) 1M 10M
1,000
0 -22
-14 -6 2 10 18 26 OUTPUT VOLTAGE ERROR (mV)
34
TIME (40 s/DIV)
TPC 19. Output Voltage Error Distribution
TPC 20. Power Supply Rejection Ratio vs. Frequency
TPC 21. No Phase Reversal
70
70
VOLTAGE NOISE DENSITY (nV/ Hz)
60 50 40 30 20 10 0 -10
VOLTAGE NOISE DENSITY (nV/ Hz)
VDD = 16V VCOM AND BUFFERS 1 TO 9 MARKER SET @ 10kHz MARKER READING = 25.7nV/ Hz
60 50 40 30 20 10 0 -10
VDD = 16V BUFFERS 10 TO 12 MARKER SET @ 10kHz MARKER READING = 36.6nV/ Hz
0
5
10 15 FREQUENCY (Hz)
20
25
0
5
10 15 FREQUENCY (Hz)
20
25
TPC 22. Voltage Noise Density vs. Frequency
TPC 23. Voltage Noise Density vs. Frequency
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ADD8702
APPLICATIONS
Figure 1 is a block diagram of the configuration of an XGAcompatible (1024 768) TFT color panel with the ADD8702 providing gamma correction reference voltages to the source drivers and an integrated VCOM driver for LCD common node.
16V BUFFER RNULL CT RL
VHIGH
A12
GMA 12
VIN11
A11
GMA 11
VIN10
A10
GMA 10
VIN9
A9
GMA 9
Figure 2. Bandwidth Measurement Information
VIN5
A5
GMA 5
16V 0.1 s BUFFER 5V 33 1k VTH VTH 10V 5V 0V
VIN4
A4
GMA 4
VIN3
A3
GMA 3
Figure 3. Transient Load Regulation Test Circuit
The ADD8702 is designed to meet the rail-to-rail capability needed by the application, yet offers the lowest cost per channel solution. The ADD8702 gamma buffers offer 10 mA continuous drive current capability. To be more competitive, the design maximizes the die area by allowing specific channels to swing to the positive rail and negative rail. So it is imperative that the channels swinging close to the supply rail be used for the positive gamma references and the channels swinging close to GND be used for the negative gamma references. The VCOM buffer can handle up to 35 mA continuous output current and can drive up to 1,000 pF pure capacitive load. Provision is available to adjust the VCOM voltage to a desired level. Refer to Figure 4 for an example of an application circuit for adjusting the output of the VCOM buffer.
VIN2
A2
GMA 2
VLOW VDD
A1
GMA 1 LCD SOURCE DRIVER
VCOM AMP LCD COMMON PLANE 32k
GND VCOM ADJUST
2k
ADD8702
Figure 4. Application Circuit
Table I. ADD8702 - 000 Mask Option, Resistor Tap Points (0 500) VDD = 12.5 V, VHIGH = 12.5 V, and VLOW = GND
Tap Point ( ) VGMA1 VGMA2 VGMA3 VGMA4 VGMA5 VGMA6 VGMA7 VGMA8 VGMA9 VGMA10 VGMA11 VGMA12 VCOM 8 57 84 115 139 194 218 298 371 418 442 488 200
Voltage 0.2 1.43 2.11 2.89 3.48 4.86 5.45 7.45 9.29 10.45 11.04 12.2 5
Unit V V V V V V V V V V V V V
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-7-
NEGATIVE GAMMA REFERENCES
Panel size and resolution determine the number of gamma reference voltages required. For a 256-grayscale level, 8-bit color scheme, 6 2 external reference nodes should be sufficient to match the characteristics of the LCD driver to the characteristics of the actual LCD panel for improved picture quality. External reference gamma correction voltages are often generated using a simple resistor ladder. Using the ADD8702, the resistor ladder is incorporated in the IC for reduced cost and number of components.
VIN8
A8
GMA 8
VIN7
A7
GMA 7
VIN6
A6
GMA 6
POSITIVE GAMMA REFERENCES
ADD8702
OUTLINE DIMENSIONS
32-Lead Lead Frame Chip Scale Package [LFCSP] (CP-32)
Dimensions shown in millimeters
5.00 BSC SQ
0.60 MAX
0.60 MAX
25 24 32 1
PIN 1 INDICATOR
PIN 1 INDICATOR
TOP VIEW
4.75 BSC SQ
0.50 BSC
BOTTOM VIEW
3.25 3.10 SQ 2.95
8
0.50 0.40 0.30
17 16
9
12 MAX
0.80 MAX 0.65 NOM
0.05 MAX 0.02 NOM
3.50 REF
1.00 0.90 0.80
SEATING PLANE
0.30 0.23 0.18
0.20 REF
COPLANARITY 0.08
COMPLIANT TO JEDEC STANDARDS MO-220-VHHD-2
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C03820-0-6/03(0)

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